Japanese Patent Application Laid-Open No. 8-158226 discloses a bulky sheet having unevenness, which is produced by entangling non-heat-shrinkable fibers and highly heat-shrinkable fibers (crimping fibers) into a unitary nonwoven fabric and heating the nonwoven fabric to develop unevenness. However, the degree of unevenness of the bulky sheet is relatively small. Further, the layer made of the crimping fibers gets denser and stiffer on being heated only to provide a sheet with considerably reduced softness. Furthermore, the heat treatment for developing the unevenness raises the cost of production.
Applicant of the present invention previously proposed a method of producing a bulky sheet comprising strengthening nonwoven fabric formed by fiber entanglement with a network sheet and shrinking the network sheet by heat application to form unevenness (see Japanese Patent Applications Laid-Open No. 5-25763 and 5-192285). The sheet obtained may be characterized by its moderate unevenness, a soft feel, and comfortable to the touch, but the method needs a heating unit for shrinking the network sheet. Additionally the pattern of the unevenness (projections and depressions) is ruled by the mesh pattern of the network sheet because the nonwoven fabric follows the shrinkage of the openings of the net to create the unevenness. Therefore, the patterns of projections and depressions that could be given to the sheet are limited.
Japanese Patent Application Laid-Open No. 4-327255 discloses a process of producing nonwoven fabric having an uneven pattern which comprises carrying a fiber aggregate on a carrier belt having patterning projections and applying high-pressure water or hot air downward to the fiber aggregate to press the fiber aggregate onto the belt thereby forming an uneven pattern while entangling the fibers. According to this technique, although nonwoven fabric with arbitrary uneven patterns or designs can be obtained, the nonwoven fabric cannot be thicker than its own thickness and is not bulky.